The present invention relates to an exposure correction method and apparatus used for making color prints from exposed color negative films.
In amateur photography, exposed color negative films often include improper exposures, which are, in general, classified into several categories, namely: underexposed negatives, over-exposed negatives, too high- or too low-contrast negatives and so forth. Even from these improper negatives, it is essential from the commercial point of view to make fine color prints with proper color balance and density. To this end, it is usual to control correctively the exposure or the proportion of the three primary color (blue, green and red) components of the printing light in accordance with the individual frames of the negative images to adjust the color balance and density. This corrective exposure control derives from R. M. Evans' theory which is disclosed in his U.S. Pat. No. 2,571,697 and is based on the observation that the proportions of the three primary color components of light-transmitting color negatives of general subjects are substantially equal to each other, that is, are constant. That is to say, the total transmitted light after integration will be gray or a certain hue close to gray. Because the hue of gray or close to gray can be obtained from equivalent exposures from blue, green and red, an exposure of each color component is correctly controlled so as to provide the equivalent exposure in color printing. This printing system is well known in the art as the LATD printing system.
Incidentally, because the exposure time for a negative depends not only on its principal part but also on its background, it is difficult to reproduce correctly the principal part from a negative whose background density is improper, namely too thick or too thin, even if the principal part of the negative is proper. Such negatives, which are hereafter called subject failure negatives, require corrective exposure when printing. For meeting this requirement, an inspection of the negatives is performed, to find the subject failure negatives and manually to set the necessary exposure correction parameters according to the nature of the failures in a printing control means before printing. The subject failure negatives are, in general, classified into two types: density failure negatives the density of whose principal part is improper, and color failure negatives the color balance of whose principal part is improper. Good examples of density failure negatives are negatives that are exposed in backlight, that include a human figure in artificial light at night, that include a human figure against a too bright background, for example sunlit snow, and so forth. On the other hand, as the color failure negatives which have a wide distribution of one specific color thereover, there can be cited as examples such negatives that are exposed with a red scene for a background, that are exposed with a green law for a background, that are exposed against the sea, and so forth.
In addition to the subject failure negatives, there are negatives which require corrective exposure when printing for making fine color prints therefrom. Some examples of these negatives are negatives that are exposed in lights other than daylight, for example light from a fluorescent lamp or from a tungsten lamp (which are in this specification referred to as special light negatives), that are under- or over-exposed to an extreme degree, or that have changed with the passage of time (the last two are in this specification referred to as unusual negatives).
In view of the above, in the conventional color printing apparatus, an exposure time is so chosen that a desirable fine color print can be made on a specific color photographic paper from a standard frame (whose negative image transmits the equivalent components of printing light for the three primary colors and has a standard density) of a specific color negative film, for example HR-100 color film (trade name of film marketed by Fuji Photo Film Co., Ltd.), which is chosen as a standard film type. The exposure time thus chosen is corrected in accordance both with the film type of the color negative film and with the negative image pattern of each frame of the color negative film.
For the above exposure time correction, the respective frames of negative images are inspected to find the exceptional frames of negative images such as the subject failure negatives, the unusual negatives, etc. and to determine the correction values necessary for these exceptional frames according to the characteristic patterns of the negative images of those frames based on experience. This correction value determination is made as to each of the three primary colors and the density for every frame and is implemented by entering the correction values into a print controller through color correction keys and density correction keys or function keys. Using the correction values together with the large area transmittance densities of the three primary colors of the frame, an actual exposure or exposure time Ti for each primary color is calculated by use of the following equation: ##EQU1## wherein i is the examined one of the three primary colors, blue, green and red
Di is the large area transmittance density of an exceptional frame PA1 DNi is the large area transmittance density of the standard frame PA1 di is a coefficient PA1 Ki is the exposure time for the standard frame PA1 D.kappa. is the difference in correction (%) between successive density correction keys PA1 Di.kappa. is the difference in correction (%) between successive color correcton keys PA1 N is the number of increments of density correction to be entered by manipulation of the density correction keys PA1 Mi is the number of increments of color correction to be entered by manipulation of the color correction keys.
It should be noted in equation (I) that the values of the characters .alpha.i, Ki depend on the types of color photographic papers to be used and on the printing sizes (enlargement rates).
In the conventional printing apparatus, the color negative film is visually inspected frame by frame by an inspector for the determination of film type. This film type determination is made based on the difference of the film in base density and the characters printed on the margin of the film. With the determination of the necessary exposure correction depending on the film type (the value of which is hereinafter abbreviated to FTDCV), the values of the necessary exposure corrections are determined for each primary color and density for each exceptional frame of the color negative film such as the subject failure negatives, the special light negatives and the like. The framedependent exposure correction values (which are hereinafter abbreviated to FDCV's) are entered by the inspector as the numbers of steps N, Mi for correction in the color printing apparatus, through the color and density correction keys. More specifically, the inspector visually observes a frame of an exceptional negative image (an exceptional frame) to determine the FDCV's according to its image pattern based on his or her experience, and then determines the numbers of steps N, Mi from the FTDCV and FDCV's by mental arithmetic.
In the conventional color printing apparatus, however, this visual inspection is extremely troublesome and is apt to lead to misjudgements of film type in case the color negative films to be inspected are of a density close to each other or similar characters or letters are printed on the margins of color negative films to be inspected. This misjudgment results in the serious drawback of producing substandard color prints which are undesirable as commercial products.